Isomerisation du Thiazole et de l'Isothiazole avant Fragmentation

Salmona, Gérard; Vincent, Émile-Jean

doi:10.1002/oms.1210130211

Cited by 9 publications

(3 citation statements)

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“…This was prepared by lithium−halogen exchange of 4-bromo-5-phenylisothiazole 6 using tert -butyllithium and quenching 4-lithio-5-phenylisothiazole 7 with CH 3 OD. The mass spectrum of the resulting product exhibited a molecular ion at m / z 162 but no signal at m / z 161, confirming complete deuteration and an intense peak at m / z 135 due to loss of H−C(3)⋮N indicating that the deuterium is located at position 4 of the isothiazole ring. , This was confirmed by the 1 H NMR spectrum which exhibited a singlet at δ 8.45 due to the H-3 proton but no signal at δ 7.40 where the C-4 proton of 1 is known to absorb …”

Section: Resultsmentioning

confidence: 79%

Photochemistry of 3- and 5-Phenylisothiazoles. Competing Phototransposition Pathways

Pavlik

Tongcharoensirikul

2000

J. Org. Chem.

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5-Phenylisothiazole undergoes phototransposition via the electrocyclic ring closure-heteroatom migration pathway and by the N(2)-C(3) interchange reaction pathway. The latter route is enhanced by the addition of triethylamine (TEA) to the reaction medium and by increasing the polarity of the solvent. In addition to phototransposition, 5-phenylisothiazole also undergoes photocleavage to 2-cyano-1-phenylethenethiol which was trapped by reaction with benzyl bromide to yield 2-cyano-1-phenylethen-1-ylbenzyl thioether. 3-Phenylisothiazole also phototransposes by both reaction pathways, but the product distribution is not affected by the addition of TEA or by changing the solvent polarity.

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Section: Resultsmentioning

confidence: 79%

Photochemistry of 3- and 5-Phenylisothiazoles. Competing Phototransposition Pathways

Pavlik

Tongcharoensirikul

2000

J. Org. Chem.

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“…GLC−MS analysis of the 4-phenylthiazole photoproduct showed a molecular ion at m / z 162 confirming that the loss of deuterium had not occurred during the photolysis. The mass spectrum also exhibited an intense signal at m / z 135 due to loss of HC-2⋮N, indicating that the deuterium is at C-5 of the 4-phenylthiazole ring. , The 1 H NMR spectrum confirmed this by exhibiting a sharp singlet at δ 8.86 where H-2 of 4-phenylthiazole is known to absorb but there is no signal for H-5 at δ 7.52 . This shows that 5-deuterio-4-phenylisothiazole ( 1b ) had been transposed to 5-deuterio-4-phenylthiazole ( 2b ) via a P 4 permutation pathway which involves only the interchange of N-2 and C-3 of the isothiazole ring.…”

Section: Resultsmentioning

confidence: 86%

“…This ambiguity was removed by studying the phototransposition chemistry of 5-deuterio-4-phenylisothiazole ( 1b ), prepared by the base-catalyzed deuteration of 4-phenylisothiazole ( 1a ). The mass spectrum of the deuterated product exhibited a molecular ion at m / z 162, consistent with monodeuteration, and an intense peak at m / z 135 due to the loss of HC-3⋮N, , indicating that the deuterium is located at ring position 5. The 1 H NMR spectrum confirmed this by showing a 1-H singlet at δ 8.75 where the C-3 proton is known to absorb but no signal at δ 8.65 where the C-5 proton is expected to appear …”

Section: Resultsmentioning

confidence: 92%

Phototransposition Chemistry of 4-Substituted Isothiazoles. The P₄ Permutation Pathway

1998

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Upon irradiation in the presence of a small quantity of base, 4-substituted isothiazoles undergo photocleavage to yield substituted cyanosulfides, which can be trapped as their benzyl thioether derivatives, and substituted isocyanosulfides. Both products are suggested to arise via initial photocleavage of the sulfur−nitrogen bond, resulting in the formation of a substituted β-thioformylvinyl nitrene, which can rearrange to the observed cyanosulfide, or cyclize to an undetected thioformylazirine. Deprotonation of the azirine leads directly to the isocyanosulfide. The plight of the isocyanosulfide depends on the C-4 substituent. If the substituent is aromatic, the isocyanosulfide is reprotonated at the isocyanide carbon and spontaneously cyclizes to a 4-substituted thiazole, the observed transposition product. If the substituent is not aromatic, the isocyanosulfide is reprotonated at sulfur and the resulting species has a higher energy barrier to cyclization. In these cases, the isocyanosulfides can be observed spectroscopically and can be trapped as their N-formylaminobenzyl thioether derivatives.

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Characterization and differentiation of heterocyclic isomers. Part 3. Study of high internal energy ions produced by electron ionization mass spectrometry on 3‐methyl‐1,2‐ and 2‐methyl‐1,3‐thiazolopyridines

Giorgi¹,

Salvini²,

Ponticelli³

et al. 1996

Journal of Heterocyclic Chem

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The eight members of two classes of heterocyclic isomers, namely 3‐methyl‐1,2‐, 1a‐d and 2‐methyl‐1,3‐thiazolopyridines 2a‐d have been characterized by mass spectrometry under electron ionization. High internal energy ions formed in the source have been studied by low and high resolution mass spectrometry. The data show remarkable differences among the various components of each class depending on the position of the nitrogen in the pyridine ring. Furthermore, by comparing the mass spectra of members of series 1 with those of their corresponding isomers belonging to series 2, it is still possible to obtain evidence for different behaviors in the fragmentation pathways. It seems to exclude the occurrence of inter‐conversion phenomena from one isomer into another, as well as conversion to a common intermediate before fragmentation. This also suggests that each member of series 1 and 2 retains its own structure after electron ionization. The data obtained on a double focusing instrument equipped with electrostatic and magnetic analyzers have been compared with those obtained on a mass spectrometer with an ion trap as the analyzer.

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Isomerisation du Thiazole et de l'Isothiazole avant Fragmentation

Abstract: The molecular ions of tfniazole and isothiazole mainly isometize to a common structure before fragmentation, as evidenced by the analysis of metastable ions abundances and kinetic energy releases.

Cited by 9 publications

References 6 publications

Photochemistry of 3- and 5-Phenylisothiazoles. Competing Phototransposition Pathways

Photochemistry of 3- and 5-Phenylisothiazoles. Competing Phototransposition Pathways

Phototransposition Chemistry of 4-Substituted Isothiazoles. The P₄ Permutation Pathway

Characterization and differentiation of heterocyclic isomers. Part 3. Study of high internal energy ions produced by electron ionization mass spectrometry on 3‐methyl‐1,2‐ and 2‐methyl‐1,3‐thiazolopyridines

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Isomerisation du Thiazole et de l'Isothiazole avant Fragmentation

Abstract: The molecular ions of tfniazole and isothiazole mainly isometize to a common structure before fragmentation, as evidenced by the analysis of metastable ions abundances and kinetic energy releases.

Cited by 9 publications

References 6 publications

Photochemistry of 3- and 5-Phenylisothiazoles. Competing Phototransposition Pathways

Photochemistry of 3- and 5-Phenylisothiazoles. Competing Phototransposition Pathways

Phototransposition Chemistry of 4-Substituted Isothiazoles. The P4 Permutation Pathway

Characterization and differentiation of heterocyclic isomers. Part 3. Study of high internal energy ions produced by electron ionization mass spectrometry on 3‐methyl‐1,2‐ and 2‐methyl‐1,3‐thiazolopyridines

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Phototransposition Chemistry of 4-Substituted Isothiazoles. The P₄ Permutation Pathway